The invention relates to a system of magnets for a selection block in textile machines, particularly a bistable system of magnets for selecting needles, magnetically operated control flaps being provided for selecting the needle allocated to the system of magnets, as well as to a selection block with such systems of magnets.
In modern knitting machines (circular knitting machines and flat knitting machines), magnet systems, which are generally combined into so-called selection blocks, are provided for selecting the needles. In order to knit a particular pattern, certain knitting needles must be selected and other needles not at a particular point in time. The selection medium is triggered electronically in modern knitting machines and it is customary to speak of an electronic selection of needles.
The desired pattern is deposited in an electronic memory and is read during the knitting of the textile part, and the needles are selected correspondingly over the interface of the selection block.
In the selection block there are energy converters, which convert the electrical triggering signal into a mechanical change in position of the control flaps, which are required for selecting the needles and protrude from the selection block. The selection blocks generally are supplied with a number of control flaps, each control flap serving one selection plane. Each control flap is provided with a cam, which interacts with needle butts or sinker butts. The control flap can assume two positions, namely, the "basic, non-selecting position" and the "working or selecting position".
In the `non-selecting` position, the sinker butts run past the control flaps and are not contacted. If a control flap is moved into the `selecting` position, the allocated sinker butt runs onto the cam and is pressed in the direction of the knitting cylinder or the needle bed. Due to the change in the position of the lifting wire, so accomplished, the condition is created mechanically so that the lifting (selecting) from the `non-knitting` position into the `knitting` or `tucking` position is brought about.
Preferably, small solenoids are used to drive and position the control flaps into the two positions.
Such a selection block is known from the EP-O 219 029-B1. However, when small solenoids are employed, which are inserted as, in themselves, independent magnetic systems into the selection block, only relatively large distances between the control flaps, which are disposed adjacent to one another or one above the other, can be realized. Accordingly, flap intervals (pitch intervals), which are significantly smaller than 5 mm, cannot be realized with the known systems. Finally, the electromagnetic capability of the driving magnets (power, change-over time, dissipated power, service life), required for the application, also depends on the volume of the electromagnet. In minimizing the volume of an optimally dimensioned electromagnet, a lower boundary is rapidly encountered, below which one cannot go. Accordingly, for a particular number of selection planes and for a particular pitch interval, the volume of the selection block is practically specified and cannot just be reduced further.
In the case of the well-known selection block, two bearings are provided for each driving system, namely one bearing for the magnet armature and one for the respective control flap. At both of these bearings, frictional losses occur. An additional place of friction, is the connection site between the magnet armature and the respective control flap, where frictional losses occur. Due to the necessary clearance in the bearings and in the connection site, there is also a not inconsiderable rebounding of the control flaps, as they reach their end positions. This rebounding is greater at higher operating speeds/cycle frequencies of the knitting machine.
In addition, the known system is constructed of a plurality of small magnets, individual parts and components, which must be adjusted specially and make the installation of the selection block expensive and cost intensive.